Double checking C-bushing degrees

[Johnnyb]

I wanted to double check and get people's opinions on the correct C-bushing angle for my build.
I have a two and a half inch spring left and a 1977 disc brake Dana 44 (Bronco OEM). I'm also running the James Duff TRO bump steer eliminator.
Now I'm going to install James Duff stock length radius arms and replace my C-bushings in the process.
The question at hand is should I use 4° or 7° C-bushings?
I thought I had determined that 7° was the right measurement but 4° is what was shipped.

THX
-JB

 

[Oldtimer]

What is the caster of front suspension?
What are pinion and drive shaft angles?

 

[DirtDonk]

And what offset, if any, do the new arms have?

 

[DirtDonk]

As you can see from the initial questions, the answer is not etched in stone by any means.

 

[Johnnyb]

Here is the readout right after I got it aligned following the installation of the tro tie rod and drag link. It drives pretty well right now. At lower speeds on city streets or mountain roads it's a little bit wandery, but on the freeway it drives like a dream.
Problem is I can't remember the degree of the C-bushings that I ordered from wild Horses with my 2.5 inch lift kit 30 plus years ago.

THX,
JB

 

[Johnnyb]

What are pinion and drive shaft angles?

I will measure this as I don't honestly know. However as far as (unlocked) down the road driveability, I am wondering if 4 degrees is the best choice.

And what offset, if any, do the new arms have?

I believe none, as they are "stock" replacements, however they are built to allow turning radius by being angled inward, with a bend near the axle to compensate. Jabes Duff website and instructions don't provide any spec for offset.

Here is a quote from the instructions, but I was double-checking and second-guessing: "NOTE: Because these radius arms have 4.25° of caster built into them, you will be able to run a lesser degreed C bushing and achieve the same caster reading. Normally a 2 or 4° C bushing can be used with a 2.5” lift and our arms."

THX,
-JB

 

[Soylent]

Do you mean the T-rex arms? I didn’t know he made stock arms. I have the T-rex with the WH 2.5” lift and use the 7 degrees.

 

[Johnnyb]

Do you mean the T-rex arms? I didn’t know he made stock arms. I have the T-rex with the WH 2.5” lift and use the 7 degrees.

Yes, T-Rex stock length arms.

 

[DirtDonk]

I believe none, as they are "stock" replacements, however they are built to allow turning radius by being angled inward, with a bend near the axle to compensate. Jabes Duff website and instructions don't provide any spec for offset.

"NOTE: Because these radius arms have 4.25° of caster built into them, you will be able to run a lesser degreed C bushing and achieve the same caster reading.

No, you found it right there. It states clearly that they are adding 4.25° of caster just the way the arms are built.
So it’s essentially the same as putting 4° bushings on stock arms.
The only thing stock about the Duff arms is their length. Meaning you don’t have to replace or relocate the frame mounts.
Nothing else is stock about them.

Is your alignment read out above, with the 77 front end? Or is it with the original? That would be a big question right there, but it may not make much of a difference in the end.
Essentially, with the addition of the radius arms, you will have almost 8° of positive caster on one side and almost 7° a positive caster on the other side. That’s more than enough to keep most people happy.

Given those readings, and your new arms, I would install 2° bushings.
Or better yet, stock (zero offset) rubber bushings. Unless you intend to take it Off Road.
If you do, then go with the 2° offset polyurethane bushings.
And hope that your opinion angle can handle the extra few degrees of tilt.

 

[Johnnyb]

No, you found it right there. It states clearly that they are adding 4.25° of caster just the way the arms are built.
So it’s essentially the same as putting 4° bushings on stock arms.
The only thing stock about the Duff arms is their length. Meaning you don’t have to replace or relocate the frame mounts.
Nothing else is stock about them.

Is your alignment read out above, with the 77 front end? Or is it with the original? That would be a big question right there, but it may not make much of a difference in the end.
Essentially, with the addition of the radius arms, you will have almost 8° of positive caster on one side and almost 7° a positive caster on the other side. That’s more than enough to keep most people happy.

Given those readings, and your new arms, I would install 2° bushings.
Or better yet, stock (zero offset) rubber bushings. Unless you intend to take it Off Road.
If you do, then go with the 2° offset polyurethane bushings.
And hope that your opinion angle can handle the extra few degrees of tilt.

Readout above is with the 77 front end. Looks like they put the wrong spec in the computer, but it drives OK.

I'm going to get it re-aligned when I have the T-Rex arms in and I am going to use a shop in Prescott which has been recommended.

THX,
-JB

 

[DirtDonk]

At this stage, the specification doesn’t really matter. It’s the result that is important.
You have 3.7 on one side and 2.5 on the other. With an unknown offset to the bushings.
If you left those bushings in and install the new arms, you would add 4.25 to those numbers. That would be 8 on one side, which is actually the specification for 78 and later Broncos and full-size pick ups. So while it’s not out of line, it’s not necessary for these vehicles either.
But you still have to start worrying about pinion angle that becomes too steep. Binding of u-joints is never good. High speed or low.

We can assume that you have 4° bushings in there now, but that’s just an assumption.
If you have 4° in there now, then I would use 4° replacements. If you have two in there now, four would be too much. And if you have seven in there now, two would be too little.
With those readings, however, I would think you have at least 2’s because 77 axles tended to have more caster built into them than earlier models.
That’s just a generalization, however, and not a universal truth. could be 4’s. Hence my next statement…
If I was doing this, I would have all three bushing sizes on hand.
Just use the appropriate one, to suit your tastes, then return the other two.

Is the vehicle still assembled at this point? Full weight on the suspension? Take a picture of your front driveshaft showing the pinion angle.

 

[Johnnyb]

At this stage, the specification doesn’t really matter. It’s the result that is important.
You have 3.7 on one side and 2.5 on the other. With an unknown offset to the bushings.
If you left those bushings in and install the new arms, you would add 4.25 to those numbers. That would be 8 on one side, which is actually the specification for 78 and later Broncos and full-size pick ups. So while it’s not out of line, it’s not necessary for these vehicles either.
But you still have to start worrying about pinion angle that becomes too steep. Binding of u-joints is never good. High speed or low.

We can assume that you have 4° bushings in there now, but that’s just an assumption.
If you have 4° in there now, then I would use 4° replacements. If you have two in there now, four would be too much. And if you have seven in there now, two would be too little.
With those readings, however, I would think you have at least 2’s because 77 axles tended to have more caster built into them than earlier models.
That’s just a generalization, however, and not a universal truth. could be 4’s. Hence my next statement…
If I was doing this, I would have all three bushing sizes on hand.
Just use the appropriate one, to suit your tastes, then return the other two.

Is the vehicle still assembled at this point? Full weight on the suspension? Take a picture of your front driveshaft showing the pinion angle.

Yes fully on the road right now I plan on tackling the project this week. I'll get a photo first thing tomorrow before I start disassembling and then I will order the 2° and 7° bushings as you suggest, it's a great idea to have all of them on hand.

-JB

 

[DirtDonk]

Luckily, they’re one of the few things that are easy to mail back. They don’t weigh 400 pounds and aren’t the size of a leaf spring!

 

[Madgyver]

7* will work. 4* may work. you decide.